Pumps are currently being used in the handling and conveying of high viscosity masses which are, for example, being delivered from barrels. In use, the locking cover of a barrel is removed. In its place, a cover is placed on the content within the barrel, that is, in contact with the pastry medium of high viscosity that is to be conveyed. The cover is then pushed into the interior of the barrel. Upon a downward movement of the cover, that is, a movement of the cover into the interior of the barrel, the medium located within the barrel is displaced in the direction of a suction opening. From this opening, the medium is removed with the help of a pump whose suction-side end is in connection with the suction opening.
Notwithstanding the foregoing pump arrangements, there are still major problems involved. Under certain operating conditions, especially, when the negative pressure is too high in relation to the viscosity of the medium, a hollow space in the shape of a bell or dome is formed below the suction opening resulting in the pump operating in a dry-run mode.
Increasing the pressure on the cover in order to displace the medium faster toward the direction of the suction opening and in greater amounts, is only possible to a limited extent. The applicable pressure is limited, for example, by the structural stability of the container and the cover. On the other hand, it is sometimes not possible to increase the suction pressure or the desired suction volume because, at the exit of the pump, a certain volume flow or a certain pressure is needed. The formation of a hollow dome or bell below the cover from which no more medium can be suctioned, is therefore, not only damaging for the pump, but also has a deleterious effect on the thereafter following work process for which a mostly continuous flow of medium is essential.
An object of the present invention is to provide a pump device which provides a reliable conveyance of medium even under unfavorable conditions of suction pressure and viscosity of the medium.